Re: [Xen-devel] [PATCH v2 01/11] vt-d: fix the IOMMU flush issue

["Xu, Quan" <quan.xu@xxxxxxxxx>]

On April 26, 2016 5:11 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >>> On 26.04.16 at 04:18, <quan.xu@xxxxxxxxx> wrote:
> > On April 25, 2016 5:22 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >> >>> On 18.04.16 at 16:00, <quan.xu@xxxxxxxxx> wrote:
> >> > --- a/xen/drivers/passthrough/vtd/iommu.c
> >> > +++ b/xen/drivers/passthrough/vtd/iommu.c
> >> > @@ -558,14 +558,16 @@ static void iommu_flush_all(void)
> >> >      }
> >> >  }
> >> >
> >> > -static void __intel_iommu_iotlb_flush(struct domain *d, unsigned long
> gfn,
> >> > -        int dma_old_pte_present, unsigned int page_count)
> >> > +static int iommu_flush_iotlb(struct domain *d, unsigned long gfn,
> >> > +                             int dma_old_pte_present,
> >> > +                             unsigned int page_count)
> >> >  {
> >> >      struct hvm_iommu *hd = domain_hvm_iommu(d);
> >> >      struct acpi_drhd_unit *drhd;
> >> >      struct iommu *iommu;
> >> >      int flush_dev_iotlb;
> >> >      int iommu_domid;
> >> > +    int rc = 0;
> >>
> >> Pointless initializer.
> >
> > I am afraid not.
> > In case I don't initialize 'rc', the compiler prints out  " error:
> > 'rc' may be used uninitialized in this function 
> > [-Werror=maybe-uninitialized]".
> 
> Looking at the patch again I can't see why that would be the case.
> Are you certain this isn't a result of subsequent patches, IOW did you try 
> this
> with just this one patch applied? 

Yes, I test it with this only patch again.

The same result.

> rc gets initialized in both the if() and the else
> branches, and there's no label allowing that initialization to be bypassed...

look at this function again, 

>> func
iommu_flush_iotlb()
{
    int rc;

    for_each_drhd_unit ( drhd )
    {
        if ()
            rc ..
        else
            rc ..
    }

    return rc;
}

<< func


The case  drhd is NULL, the rc  may be not initialized.

Development ENV:
 Ubuntu 14.04.1,
 GCC 4.8


Quan



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